Isolate-Specific Detection of Grapevine fanleaf virus from Xiphinema index Through DNA-Based Molecular Probes

Development of PCR and TaqMan PCR Assays to Detect Pseudomonas coronafaciens, a Causal Agent of Halo Blight of Oats

Pseudomonas coronafaciens causes halo blight on oats and is a plant quarantine bacterium in many countries, including the Republic of Korea. Using of the certificated seed is important for control of the disease. Since effective detection method of P. coronafaciens is not available yet, PCR and TaqMan PCR assays for specific detection of P. coronafaciens were developed in this study. PCR primers were designed from the draft genome sequence of P. coronafaciens LMG 5060 which was obtained by the next-generation sequencing in this study. The PCR primer set Pc-12-F/Pc-12-R specifically amplified 498 bp from the 13 strains of P. coronafaciens isolated in the seven different countries (Canada, Japan, United Kingdom, Zimbabwe, Kenya, Germany, and New Zealand) and the nested primer set Pc-12-ne-F/Pc-12-ne-R specifically amplified 298 bp from those strains. The target-size PCR product was not amplified from the non-target bacteria with the PCR and nested primer sets. TaqMan PCR with Pc-12-ne-F/Pc-12-ne-R and a TaqMan probe, Pc-taqman, which were designed inside of the nested PCR amplicon, generated Ct values which in a dose-dependent manner to the amount of the target DNA and the Ct values of all the P. coronafaciens strains were above the threshold Ct value for positive detection. The TaqMan PCR generated positive Ct values from the seed extracts of the artificially inoculated oat seeds above 10 cfu/ml inoculation level. PCR and TaqMan PCR assays developed in this study will be useful tools to detect and identify the plant quarantine pathogen, P. coronafaciens.

Detection of Nepovirus Vector and Nonvector Xiphinema Species in Grapevine

Fanleaf degeneration is considered the most damaging viral disease of grapevine. The two major nepoviruses involved are Grapevine fanleaf virus (GFLV) and Arabis mosaic virus (ArMV) which are respectively and specifically transmitted by the dagger nematodes Xiphinema index and X. diversicaudatum. The methods described below are aimed at detecting four prevalent grapevine Xiphinema species: the vector species previously mentioned and two nonvector species X. vuittenezi and X. italiae.

Quantitative field testing Heterodera glycines from metagenomic DNA samples isolated directly from soil under agronomic production

A quantitative PCR procedure targeting the Heterodera glycines ortholog of the Caenorhabditis elegans uncoordinated-78 gene was developed. The procedure estimated the quantity of H. glycines from metagenomic DNA samples isolated directly from field soil under agronomic production. The estimation of H. glycines quantity was determined in soil samples having other soil dwelling plant parasitic nematodes including Hoplolaimus, predatory nematodes including Mononchus, free-living nematodes and biomass. The methodology provides a framework for molecular diagnostics of nematodes from metagenomic DNA isolated directly from field soil.

Quantitative field testing Rotylenchulus reniformis DNA from metagenomic samples isolated directly from soil

A quantitative PCR procedure targeting the β-tubulin gene determined the number of Rotylenchulus reniformis Linford & Oliveira 1940 in metagenomic DNA samples isolated from soil. Of note, this outcome was in the presence of other soil-dwelling plant parasitic nematodes including its sister genus Helicotylenchus Steiner, 1945. The methodology provides a framework for molecular diagnostics of nematodes from metagenomic DNA isolated directly from soil.

Detection of Tomato black ring virus by real-time one-step RT-PCR

A TaqMan-based real-time one-step RT-PCR assay was developed for the rapid detection of Tomato black ring virus (TBRV), a significant plant pathogen which infects a wide range of economically important crops. Primers and a probe were designed against existing genomic sequences to amplify a 72 bp fragment from RNA-2. The assay amplified all isolates of TBRV tested, but no amplification was observed from the RNA of other nepovirus species or healthy host plants. The detection limit of the assay was estimated to be around nine copies of the TBRV target region in total RNA. A comparison with conventional RT-PCR and ELISA, indicated that ELISA, the current standard test method, lacked specificity and reacted to all nepovirus species tested, while conventional RT-PCR was approximately ten-fold less sensitive than the real-time RT-PCR assay. Finally, the real-time RT-PCR assay was tested using five different RT-PCR reagent kits and was found to be robust and reliable, with no significant differences in sensitivity being found. The development of this rapid assay should aid in quarantine and post-border surveys for regulatory agencies.

The use of collagenase to improve the detection of plant viruses in vector nematodes by RT-PCR

Tomato ringspot virus (ToRSV), Tobacco ringspot virus (TRSV) and Tobacco rattle virus (TRV) are transmitted to healthy plants by viruliferous nematodes in the soil. A method was developed for extraction of genomic viral RNA from virus particles carried within nematodes and a sensitive nested RT-PCR detection assay. The procedure has been adapted to microscale for handling multiple samples. This assay is effective for detection of ToRSV or TRSV in Xiphinema americanum or TRV in Paratrichodorus allius. With this method, viruses can be detected in nematodes fed on infected plants or from field-collected nematodes where the percentage of viruliferous nematodes is unknown. Soil samples from four red raspberry fields infected with ToRSV were collected in 2003 and 2004. Nematodes isolated from these samples were assayed for ToRSV by RT-PCR and compared to cucumber baiting bioassay for virus transmission from the same soil samples. ToRSV was detected in nematodes throughout the season with similar frequencies by the RT-PCR assay and the transmission bioassay.